1. Field of the Invention
The present invention relates to glass compositions for making glass fibers, and more particularly to glass compositions having lowered liquidus and forming temperatures.
2. Technical Considerations
The most common glass composition for making continuous glass fiber strands for textiles and glass fiber reinforcements is xe2x80x9cExe2x80x9d glass. The requirements as to what type of composition constitutes an E-glass composition are included in ASTM D578-98. An advantage of using E-glass is that its liquidus temperature is well below its forming temperature, i.e. typically greater than 100xc2x0 F. (56xc2x0 C.) and generally between 150xc2x0 F. (83xc2x0 C.) to 200xc2x0 F. (111xc2x0 C.). As used herein, the terms xe2x80x9cforming temperaturexe2x80x9d and xe2x80x9cTFORMxe2x80x9d mean the temperature of the glass at which the viscosity of the glass is log 3, or 1000 poise, and the terms xe2x80x9cliquidus temperaturexe2x80x9d and xe2x80x9cTLIQxe2x80x9d mean the temperature at which solid phase (crystals) and liquid phase (melt) are in equilibrium. The difference between TFORM and TLIQ, referred to herein as xe2x80x9cdelta Txe2x80x9d or xe2x80x9cxcex94Txe2x80x9d, is a common measure of the crystallization potential of a given melt composition. In the glass fiber forming industry, xcex94T is typically maintained at a temperature of at least 90xc2x0 F. (50xc2x0 C.) in order to prevent devitrification of the molten glass in the bushing area of a glass fiber forming operation.
Boron and fluorine containing glass were developed to meet these operating conditions. More specifically, the boron and fluorine were included in the glass batch materials to act as fluxes during the glass melting operation. However, these materials are volatilized during melting and boron and fluorine emissions are released to the atmosphere. Since boron and fluorine are considered pollutants, these emissions are closely controlled by environmental regulations, which, in turn, requires careful control of the furnace operations and the use of expensive pollution control equipment. In response to this, low boron and/or low fluorine E-glasses were developed. As used herein, xe2x80x9clow boronxe2x80x9d means that the glass composition is no greater than 5 weight percent boron, and preferably boron-free and xe2x80x9clow fluorinexe2x80x9d means that the glass composition is no greater than 1 weight percent fluorine, and preferably is fluorine-free.
For example, U.S. Pat. No. 3,929,497 discloses a boron-free and fluorine-free glass composition containing titanium dioxide in the range of 0.5 to 5 percent by weight and Fe2O3 in the range of 5 to 15 percent by weight.
U.S. Pat. No. 4,199,364 discloses a boron-free and fluorine-free glass composition that contains Li2O in the range of 0.1 to 1.5 percent by weight and may also include barium oxide. The liquidus temperature of the compositions is over 2200xc2x0 F.
U.S. Pat. No. 4,542,106 discloses a boron-free and fluorine-free glass composition that contains 1 to 5 percent by weight TiO2. The fibers also have a seed count of 5 seeds or less per cubic centimeter of glass and an electrical leakage value of 2.8 nanoamperes or less.
U.S. Pat. No. 5,789,329 discloses a boron-free and fluorine-free glass composition that contains up to 0.9 percent by weight TiO2 and has a xcex94T of at least 100xc2x0 F. (56xc2x0 C.).
For additional information concerning glass compositions and methods for fiberizing the glass composition, see K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (3d Ed. 1993) at pages 30-44, 47-60, 115-122 and 126-135, and F. T. Wallenberger (editor), Advanced Inorganic Fibers: Processes, Structures, Properties, Applications, (2000) at pages 81-102 and 129-168, which are hereby incorporated by reference.
Because the actual fiber forming operation is conducted at high temperatures, there are high energy costs associated with its production. In addition, the high temperatures accelerate the degradation of the refractory used in the glass melting furnace as well as the bushings used to form the fibers. The bushings include precious metals that cannot be recovered from the glass as the bushings corrode. It would be advantageous to produce the glass fibers at the lowest possible forming and liquidus temperatures so as to reduce the energy costs and thermal load on the furnace refractory and bushings, while at the same time provide the xcex94T required to ensure an uninterrupted glass fiber forming operation. Reducing the forming and liquidus temperatures of the glass compositions can also result in environmental benefits, such as but not limited to, a reduction in the amount of fuel required to generate the energy necessary for the fiber forming operation, as well as a reduction in the flue gas temperature. In addition, it would be advantageous if the glass compositions are low fluoride and/or low boron compositions, and preferably are fluorine-free and/or boron-free, so as to reduce or eliminate the environmental pollutants associated with these materials.
The present innovation provides a glass fiber composition comprising: 52 to 62 percent by weight SiO2, 0 to 2 percent by weight Na2O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al2O3, 0.05 to 0.80 percent by weight Fe2O3, 0 to 2 percent by weight K2O, 1.7 to 2.9 percent by weight MgO, 0 to 10 percent by weight B2O3, 0 to 2 percent by weight TiO2, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO2, and 0 to 2 percent by weight SrO, wherein the glass composition has a forming temperature of no greater than 2280xc2x0 F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155xc2x0 F. In one nonlimiting embodiment of the invention, the glass fiber composition further includes at least one material selected from the group consisting of: 0.05 to 1.5 percent by weight Li2O, 0.05 to 1.5 percent by weight ZnO, 0.05 to 3 percent by weight MnO, and 0.05 to 3 percent by weight MnO2.
The present invention also provides a glass fiber composition consisting essentially of: 52 to 62 percent by weight SiO2, 0 to 2 percent by weight Na2O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al2O3, 0.05 to 0.80 percent by weight Fe2O3, 0 to 2 percent by weight K2O, 2.2 to 2.9 percent by weight MgO, 0 to 10 percent by weight B2O3, 0 to 2 percent by weight TiO2, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO2, and 0 to 2 percent by weight SrO, wherein the glass composition has a forming temperature of no greater than 2280xc2x0 F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155xc2x0 F.
The present innovation provides a glass fiber composition comprising: 52 to 62 percent by weight SiO2, 0 to 2 percent by weight Na2O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al2O3, 0.05 to 0.80 percent by weight Fe2O3, 0 to 2 percent by weight K2O, 1.7 to 2.6 percent by weight MgO, 0 to 10 percent by weight B2O3, 0 to 2 percent by weight TiO2, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO2, and 0 to 2 percent by weight SrO, and further including at least one material selected from the group consisting of: 0.05 to 1.5 percent by weight Li2O, 0.05 to 1.5 percent by weight ZnO, 0.05 to 3 percent by weight MnO, and 0.05 to 3 percent by weight MnO2, wherein the glass composition has a forming temperature of no greater than 2280xc2x0 F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155xc2x0 F. In one nonlimiting embodiment of the invention, the SiO2 content is 57 to 59 percent by weight, the Na2O content is up to 1 percent by weight, the CaO content is 22 to 24 percent by weight, the Al2O3 content is 12 to 14 percent by weight, the Fe2O3 content is up to 0.4 percent by weight, and the K2O content is up to 0.1 percent by weight, and the composition includes at least one material selected from the group consisting of: 0.2 to 1 percent by weight Li2O, 0.2 to 1 percent by weight ZnO, up to 1 percent by weight MnO, and up to 1 percent by weight MnO2.